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EW_Advance_20210421 > Week 1 > Flashcards

Week 1 Flashcards

1
Q

What is the EM Spectrum?

A

The complete range of frequencies of natural and man-made radiation.

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2
Q

What is EM Radiation?

A

Energy waves produced by the oscillation or acceleration of an electrical charge.

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3
Q

Name 2 Components of an EM Wave.

A
  1. Electrical

2. Magnetic.

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4
Q

Explain the military’s main uses of the EM spectrum. (x4)

A
  1. Radio communications
  2. Primary and secondary radar
  3. IR detection
  4. Ultraviolet seekers.
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5
Q

What does RADAR stand for?

A

Radio Detection And Ranging.

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6
Q

What is the speed of light in m per second?

A

300,000,000m per second

3 x 10^8.

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7
Q

Explain the relationship between wavelength and frequency.

A

Inversely proportional.

  • The longer the wavelength the lower the frequency
  • The shorter the wavelength the higher the frequency.
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8
Q

Polarisation is determined by the orientation of which field?

A

The Electric Field.

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9
Q

State the relationship between power density and range.

A

Power density will decrease, as the range from the source increases.

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10
Q

State the two forms of atmospheric attenuation.

A

Absorption and Scattering.

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11
Q

Explain Atmospheric Absorption.

A

Atmospheric Absorption occurs when the energy from the EM wave dissipates as it interacts with gas molecules. The molecules absorb the radiation.

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12
Q

Explain Atmospheric Scattering.

A

Atmospheric scattering occurs when EM waves hit molecules in the atmosphere and change their direction as a result.

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13
Q

Explain diffraction in relation to propagation.

A

Diffraction is the term used for the bending of waves around the edges of objects such as buildings and mountains. Longer wavelengths are diffracted more than shorter wavelengths.

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14
Q

Explain reflection in relation to propagation.

A

Reflection is the term used for the reflection of waves off any surface.

The angle of incidence equals the angle of reflection, as measure from the normal to the surface.

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15
Q

Explain refraction in relation to propagation.

A

The variation of the speed of an EM wave, dependant on the density of the medium it travels through; the denser the medium the slower the speed of the wave.

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16
Q

State the different wave types. (x3)

A
  1. Ground Wave (Surface + Space)
  2. Space Wave
  3. Sky Wave.
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17
Q

State the factors affecting a Space Wave. (x3)

A
  • Attenuation, scattering, reflections from objects
  • Average path-length is restricted to around 25 to 40km
  • For longer distances relay stations are required.
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18
Q

Which layers of the earth’s atmosphere have a major effect on the performance of EM waves? (x2)

A
  • Ionosphere

- Troposphere.

19
Q

State the factors that affect Radar. (x8)

A
  • Frequency
  • PRF
  • PW
  • Power
  • Beamwidth
  • ARP
  • Antenna
  • Weight.
20
Q

What target information can we get from Radar? (x6)

A
  • Range
  • Bearing
  • Height
  • Course
  • Speed
  • Shape/size/outline.
21
Q

State the different types of Radar display. (x3)

A
  • Plan Position Indicator (PPI)
  • B-scope
  • A-scope.
22
Q

Explain Bandwidth.

A

The difference between the upper and lower frequencies, usually measured in Hz.

23
Q

What external factors will affect signal quality? (SNR) (x4)

A
  • Distance from source
  • Atmospheric conditions, sunspot activity
  • No line of sight, multi-path interference
  • Jamming.
24
Q

How can height information be obtained from a circular scanning radar?

A

By using 2 beams, 1 verticle and 1 at 45 degrees, creating a V-beam.

25
Q

How does a search radar calculate aircraft height using V-beam?

A

By measuring the time difference between each beam. The longer the time interval, the higher the target.

26
Q

Name the 2 types of Sector Scan.

A
  • Bi-directional Sector Scan

- Uni-directional Sector Scan.

27
Q

What are the advantages of using a pencil beam? (x3)

A
  • Higher power
  • Small bandwidth
  • Good tracking information.
28
Q

Describe a Raster Scan.

A

The beam sweeps each bar horizontally, then drops/rises to the next bar.

Once the whole frame has been scanned, the beam slews to the start and repeats.

29
Q

Describe a monopulse radar.

A

Transmits out one pulse.

The received pulse is split into parts, then the signal strength is compared.

30
Q

State what an ES receiver should do. (x4)

A
  • Intercept
  • Measure
  • Identify
  • Display.
31
Q

Describe Amplitude Comparison.

A

Where ever the amplitude is ‘loudest’ is where the source is coming from.

32
Q

Describe Phase Comparison.

A

Uses the difference in phase from the same signal to work out direction. A time delay is used to put the signals in phase. The time delay is then used to calculate the relative DoA.

33
Q

Describe unintentional pulse modulation and how it is used.

A

Unintentional pulse modulation is caused by system noise and/or different operation/installation of components and helps with Specific Emitter Identification (SEI).

34
Q

Explain the characteristics and limitations of a Co-axial cable.

A
  • Co-ax traditionally not suitable for high frequency / high power application
  • Generally, over 1GHz co-ax becomes problematic
  • Flashover and arcing can occur with high power
  • Internal impedance losses can be high
  • Over 36GHz high attenuation means almost impossible
  • Flexible.
35
Q

Explain the characteristics and limitations of a Waveguide.

A
  • Waveguide suffers almost no losses
  • Used to be heavy but now are electroplated plastics
  • Signals are shielded
  • Inflexible.
36
Q

Explain the term ‘sidelobe’ in relation to the main beam.

A

Energy reflected near the parabola edges produces extra lobes of RF energy radiating out from the antenna.

37
Q

Name the two methods of beam steering.

A
  • Mechanical

- Electronic.

38
Q

Describe mechanical beam steering.

A

The beams are steered by the rotation of the antenna.

Aircraft radar will tilt the main array to increase the radar Field of View.

39
Q

Describe electronic beam steering and its advantage over mechanical beam steering. (x3)

A
  • Phase
  • Frequency
  • Time delay

Electronic scanning has the advantage that it is much quicker and more agile than mechanical methods.

40
Q

Explain Signal to Noise Ratio (SNR).

A

The radar’s ability to see targets in the presence of noise.

41
Q

Explain Bandwidth.

A

The difference between the upper and lower frequencies. Typically measured in Hz.

42
Q

Describe the external factors affecting signal quality. (x4)

A
  • Distance from source
  • Atmospheric conditions
  • Sunspot activity
  • Jamming
43
Q

Describe the external factors affecting signal quality.

A

Receiver noise is the source of most of the noise as it is amplified along with the signal.

EW_Advance_20210421 (4 decks)

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